Initially it was just a paid download for the text of the Bible.

With more research in the App Store though I realized audio Bibles were selling much more than I was.

So I outsourced the audio (mentioned in the post I think) and now the model is that users download the original app (with the text) for free, and then can buy the audio as an IAP.

This works great on multiple fronts: I collect more email address, I rank better in search because I get more downloads, and the audio sells better as an IAP than as a stand alone app.